Empirical Earth · Shape, Curvature & the Horizon

Eratosthenes measured the globe with two sticks — and a flat Earth fails his test

The claim

“Eratosthenes’ shadows are explained by a small, nearby Sun over a flat Earth.”

What is measured

With two sticks and one shadow angle, Eratosthenes got Earth’s circumference within a few percent of 40,008 km. The flat-Earth “close Sun” reading only holds while you take just two measurements. A third one, or a second city pair, forces a straight line and one consistent globe, never one consistent plane. For how the horizon and the drop scale with distance, see curvature and the horizon.

What would show this is wrong

noon shadow angles that grow in a curved way with north–south distance, or city pairs that give different circumferences. Either would point to a near Sun over a plane. Both are the opposite of what is measured.

Sources

  1. Eratosthenes’ measurement of Earth’s circumference. Around 240 BC Eratosthenes compared the noon solstice Sun at Syene (overhead, no shadow) and Alexandria (a gnomon shadow of ~7.2°, one-fif link
  2. Spherical Earth: the method, its assumptions and reproductions. Eratosthenes’ result depends on the Sun’s rays being effectively parallel (a distant Sun); repeated at several latitudes the n link
  3. Eratosthenes, crowdsourced. The debunker SciManDan had viewers worldwide measure a vertical stick’s shadow at local noon on the summer solstice; plotted against latitude the ratios followed link
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